I got a better coach but i still cannot train my players further

You should look for a better "Basic" trainer to start with.

Indeed, there are several types of coaches and each type has his own set of exercises. Your team's default coach is a "Basic" coach and unlocks an exercise for each ability. The other types of coaches ("Technique", "Physique", etc.) do not improve the default exercises but unlock new ones. See "How to unlock new exercises" for more information.